1.5-μm infrared excitation of visible luminescent in Y1−<i>x</i>Er<i>x</i>F3 and Y1−<i>x</i>−<i>y</i>Er<i>x</i>Tm<i>y</i>F3 via resonant-energy transfer

Abstract

Intense visible emission in the red, green, and blue has been observed from infrared to visible multiphoton Y1−xErxF3 upconversion phosphors pumped with 1.5-μm radiation from InGaAsP-laser sources. With 0.01&amp;lt;x&amp;lt;0.2, the dominant emission is in the green corresponding to transitions from the 4S3/2 level of Er3+. The addition of Tm3+ in the 0.001–0.02 range preferentially quenches the emission from the higher-energy Er3+ levels resulting in a red visible emission originating on the Er3+ 4F9/2 level. The phosphors are useful visible monitors of focused 1.5-μm semiconductor laser and unfocused F-center laser radiation. The unexpectedly high brightness in the visible may be attributed to thermal equilibration, where the excitation is trapped in the higher lying states after each upconversion step.